HK1111525B - Planar antenna for mobile satellite applications - Google Patents

Description

Planar antenna for mobile satellite applications

Technical Field

The present invention relates generally to antennas for vehicular mobile applications utilizing mobile satellite systems, and more particularly to a microstrip fed loop patch antenna (fed annular patch antenna) having a tapered radiation pattern with high directivity in a low elevation range above the horizon. Such antennas are typically designed as roof-top (car-top) antennas for satellite communications. The invention also relates to a multi-system antenna (multi-system antenna).

Background

In recent years, many new satellite-based services for vehicles (automobiles, airplanes, etc.) have been put into use. These services include many applications such as satellite communications or global positioning systems. A small antenna, usually located on the roof of the vehicle, is required to receive these types of services as well as traffic and emergency or safety information data. Not only are these services likely to operate on different frequencies, but the radiation pattern requirements of the antennas are also different. For example, telecommunications may be provided via a geostationary satellite system which requires the antenna beam to be at an elevation angle between 20 ° and 60 ° at european latitudes, whereas a global positioning system requires the antenna beam to be at zenith elevation angles.

The development of an efficient vehicle front end requires antennas with high directivity at the desired elevation angle, flat curves, light weight, low cost, and preferably suitable for curved surfaces.

Schemes using omni-directional antennas are not envisaged due to their low gain. Another solution using phased array composition for tracking satellites is not envisaged either, since it is too expensive for standard consumer terminals. For these front-end circuit developments of antennas for vehicle mobile applications, printed antennas are of course the most suitable antenna type.

The requirements of the user terminal antennas depend strongly on the relevant spatial segment. Several existing and foreseeable services will be based on geostationary spatial segments, which require moderate gains (2-3 to 6-7 db) for the user segment antennas. The common user segment antennas used for these applications can be divided into two main subsets: low latitude and high latitude. Low altitude applications require antennas with a wide beam pointing in the vertical direction and their design is not without any particular difficulties. At high latitudes, geostationary satellites can be seen at elevation angles between 66 ° and 22 °. In this case, a user antenna for mobile applications must have maximum directivity at an elevation angle of about 45 ° and it must be omnidirectional in azimuth. In other words, these user antennas must have a conical radiation pattern.

Printed antennas that produce a conical radiation pattern are of great interest for the design of planar user terminal antennas for mobile satellite systems. Circular and annular patches that resonate in higher modes are also common candidates for acquiring such radiation patterns.

One prior art solution is disclosed in us patent application 2003/0210193. This document relates to a low profile disc-shaped two-antenna assembly 100, as shown in figure 11, comprising a first circularly polarised loop antenna and a second rectilinear monopole antenna located concentrically within the loop antenna. The antenna assembly 100 occupies a cylindrical volume having a central axis.

The loop antenna includes a second order mode (TM) tuned to operate₂₁) Is fed by a metallic feeding column 103 and a capacitor 104 in series therewith. The loop antenna is dielectrically loaded to reduce its physical size by placing a low dielectric constant plastic or dielectric ring 107 beneath the resonant ring 101. The monopole antenna comprises two metal posts 105 located on opposite sides of the central axis and a metal disc 106 supported at the top end of the metal posts. Mechanical support for the feed post 103, the metal monopole post 105, and the metal ground plane 109 is provided by the PCB 108.

Both the loop and monopole radiate with a cone radiation pattern whose axis is generally perpendicular to the top planar surface of the antenna assembly 100, which includes the metallic resonating ring 101 and the metallic disk 106.

However, U.S. patent application 2003/0210193 shows some drawbacks. First, as mentioned previously, one of the most important requirements for a user terminal antenna for mobile satellite communications is an antenna having a cone-shaped radiation pattern at the desired elevation angle, i.e. for example between 20 ° and 60 °, in the center of the desired area, for example about 40-45 °. In the antenna assembly shown in us patent application 2003/0210193, the loop and monopole antennas are both excited via metallic feed stubs 103 and 105, wherein the metallic feed stubs 103 and 105 extend between the ground plane 109 and the corresponding radiating elements 101 and 106.

It has been shown within the scope of the present invention that such metallic feed pillars introduce perturbations in the tapered radiation pattern. The resulting pattern is less homogenous than theoretically expected and the radiation amplitude is reduced. Therefore, the resulting antenna is less efficient.

Further, for the purpose of integrating such an antenna assembly in a vehicle roof application, the behavior of this antenna assembly will be significantly affected depending on whether the vehicle roof material is glass, metal or plastic, and depending on whether the vehicle roof design is flat, curved or has any other varied shape. Because the antenna disclosed in U.S. patent application 2003/0210193 relies on a ground plane, it is necessary to adjust the antenna radiation pattern using a metal base.

Disclosure of Invention

The main object of the present invention is to overcome the above mentioned drawbacks by providing an antenna assembly with a low attitude, which can be arranged very close to or even in contact with any type of mobile support, and which has a homogenous conical radiation pattern with satisfactory efficiency.

To achieve the above object, the present invention relates to an antenna assembly according to claim 1. Thus, a more homogenous cone radiation pattern is obtained by means of the feed line which supplies or receives signal energy to or from the patch radiating element in a non-contact manner through the opening (opening). However, the non-contact coupling prevents the use of a metal base connected to the first electrical ground. It is therefore further provided with an additional foam layer or air layer arrangement, and a second ground plane, which enables the effects caused by the vehicle cradle in which the antenna assembly is embedded to be significantly reduced, and makes it possible to reduce the minimum required distance between the vehicle and the antenna assembly.

Further advantageous features are considered in the dependent claims. For example, the use of a specific dielectric layer allows for optimized radiation at low elevation angles and further reduces the size of the antenna. Further, by utilizing a feed line slot connected with the patch radiating element, the antenna bandwidth can be increased compared to excitation through a feed post according to prior art solutions. Furthermore, by utilizing a particular slot deployment arrangement, the circular polarization is particularly efficient.

Another object of the present invention relates to a planar multifunction antenna system for vehicle terminals, which is able to simultaneously satisfy the requirements of several mobile satellite system applications.

To achieve said other object, the invention also relates to a multi-system antenna assembly according to claim 19. The idea is in particular to integrate other elements using the space left by the central part and/or the periphery of the ring, so that different systems can be accessed without increasing the size and production costs.

Advantageous features of the multi-system antenna assembly are given in the dependent claims.

Drawings

The foregoing and other objects, features and advantages of the invention will be apparent from the following detailed description of preferred embodiments, as illustrated in the accompanying drawings, in which:

fig. 1A is a cross-sectional view of a single antenna element (single antenna assembly) according to a first embodiment of the present invention;

fig. 1B is a schematic top view of a single antenna component according to the first embodiment with its layout overprinted (overprinted);

fig. 2 is a cross-sectional view of a single antenna assembly according to a first variation of the second embodiment of the invention;

fig. 3 is a cross-sectional view of a single antenna component according to a second variant of the second embodiment of the invention;

fig. 4 is a cross-sectional view of a single antenna component according to a third variant of the second embodiment of the invention;

fig. 5 is a schematic top view of the slot arrangement towards the radiating element;

fig. 6 is a cross-sectional view of a single antenna assembly according to a third embodiment of the present invention;

FIG. 7 is a top view of a first multi-system antenna assembly according to any preceding embodiment of the invention;

figure 8 is a cross-sectional view of a second multi-system antenna component according to the first embodiment of the invention;

FIGS. 9A-9B illustrate different possible shapes of a dielectric substrate (dielectric substrate);

FIGS. 10A-10C illustrate different possible shapes of the slot;

as mentioned, fig. 11 is a three-dimensional view of a two-antenna assembly according to the prior art.

Detailed Description

It is noted first that the figures are given only for the purpose of illustrating several embodiments which will be described hereinafter, and that the cross-sectional views of different antenna components are divided into different layers and they are not necessarily represented on the same scale in the same figure.

In the following embodiments, the antenna assembly is a microstrip patch antenna for mobile satellite communications, preferably in the second order mode (TM)₂₁) The resulting calculated radiation patterns are described in detail in a published paper entitled "circular polarized systematic patterns from circular microstrip antennas" (IEEE Transactions and antennas propagation, vol. ap-32, No. p, September 1994), which is incorporated herein by reference.

Fig. 1A is a cross-sectional view of a single antenna assembly according to a first embodiment of the present invention. According to the described structure, the antenna component 1 preferably occupies a thin disc-shaped or cylindrical volume having a central axis (D) and a height that can be divided into successive layers, each being circular or annular.

Moving away from the top of fig. 1A, the antenna assembly 1 comprises a ring-shaped patch radiating element 2, preferably printed or etched on an annular epoxy film forming a first layer L1, said first layer L1 ensuring that the patch radiating element 2 is fixed throughout the antenna assembly. An annular epoxy film L1 is adhered to a first dielectric substrate layer L2 formed of a plastic material. However, the annular epoxy film L1 may be omitted and the patch radiating element 2 directly glued to the plastic layer L2. According to the embodiment shown in fig. 1A, the plastic layer L2 is annular in shape with a disc-shaped void 3 in the middle. However, as described later with respect to fig. 9A-9B, this plastic layer L2 may have a different shape that is capable of changing its behavior.

Beneath the first dielectric layer L2, there is a second dielectric layer L3, preferably made of polytetrafluoroethylene, commonly referred to as PTFE. The second dielectric layer L3 is metallized on both sides. The upper metal plane 4, separating the first dielectric layer L2 from the second dielectric layer L3, is used as a first electrically conducting ground plane 4 for the antenna assembly 1, while the lower metal plane 5 is used to support the microstrip circuitry of the antenna, which includes the lines 6, connectors (not shown), active elements (also not shown), etc. The different elements forming the microstrip circuit are well known to the person skilled in the art and are therefore not described in detail here, the design of which depends on the specific desired application. The metal planes 4 and 5 can be used to simultaneously etch at least one opening 7, preferably a slot, and the microstrip circuit has in particular at least one microstrip or feed line 6, respectively.

It is important to note that the first dielectric layer L2 is disposed between the opening 7 and the patch radiating element 2, and the feed line 6 supplies or receives signal energy to or from the patch radiating element 2 through the opening 7 in a non-contact manner.

The above-described assembly forms a microstrip patch antenna for mobile satellite communications that is designed to be advantageously arranged in a rooftop application. However, in the present invention it has been demonstrated that such an antenna assembly 1 is significantly affected by the material and shape of the vehicle roof. In practice, the behaviour of such an antenna assembly arranged directly on the vehicle roof may vary significantly depending on whether the material of the vehicle roof is metal, glass or plastic, and whether the shape of the vehicle roof is planar or curved. Therefore, to ensure a homogenous behavior of slot-coupled (slot-coupled) antenna assemblies, it is necessary to provide a gap of at least 25 millimeters (mileter) between the antenna and the vehicle roof. Of course, such a void requirement is unacceptable to automotive manufacturers. Therefore, in order to eliminate such a requirement for a gap between the antenna and the vehicle roof, a third dielectric layer L4, such as a layer of air or foam, is provided, under which the second ground plane 8, which is a rear shield, is placed. The third dielectric layer L4 associated with the second ground plane 8 makes it possible to place the antenna component directly on the vehicle roof or even to embed it inside.

Fig. 1B is a top view of a single antenna assembly according to the first embodiment shown in fig. 1A. For simplicity, only some of the layers of the antenna of fig. 1A are shown.

We find a ring patch radiating element 2 supported by an epoxy film L1 mounted over a first dielectric substrate L2 (not visible). As mentioned before, said first electrically conducting ground plane (not shown) has at least one opening 7 which is slot-shaped and at least partly faces the annular patch radiating element 2. Thus, at least one feed line 6 is slot-coupled to the annular patch radiating element 2.

In order to obtain a dual Circular Polarization (CP), i.e. with both left and right circular polarizations, two excitation points need to be placed along the patch radiating element, and therefore the electrically conductive ground plane preferably comprises two slots 7 and it is below two microstrip lines 6 fed through a hybrid connector. The slots 7 are angularly displaced to obtain left and right circular polarizations. The slot 7 is advantageously placed along the annular patch 2 at an angle of 135 ° to the central axis (D). However, it is also possible to obtain these two circular polarizations by placing the two excitation slots at an angle of 45 °, however, the resulting cone beam will lack homogeneity, i.e. the level of directivity of the cone cut along the radiation pattern will fluctuate. Furthermore, in order to optimize the homogeneity of the radiation pattern in azimuth, the slots are preferably etched in a circular ground plane. It is noted that a four slot variation is also possible. The two further grooves are then placed symmetrically with respect to the central axis (D).

Considering again fig. 1A, in order to increase the bandwidth and efficiency of the antenna, a relatively thick dielectric layer L2 needs to be used between the annular patch radiating element 2 and the electrically conducting ground plane 4. In said first embodiment, this layer L2 consists, for example, of a plastic ring or a disc eventually made of, for example, 6 mm plastic. On this plastic layer, an epoxy film L1, on which the patch has been printed or etched, may be adhered.

A long slot 7 is required to couple energy from the microstrip line 6 to the patch radiating element 2. The required size of a standard rectangular slot will be larger than the width of the annular patch 2, which will increase the degree of coupling between the excitation ports, i.e. the slots, and thus will reduce the quality of the circular polarization.

Therefore, to avoid this problem, special slots with folding arms have been devised. Preferably, each slot 7 is folded until it completely faces the annular patch radiating element 2. Fig. 10A-10C illustrate some possible designs.

According to a preferred example of the above first embodiment, an array of heights with different layers (L1-L4) is given below. And also gives the dielectric constant (Dc), also called permittivity, of each layer.

Layer(s)	Material	Thickness (millimeter)	Dc
				1	Epoxy resin	0.1	4.4
2	Plastic material	6	2.3
				3	PTFE	0.5	2.49
4	Foam (or air)	5	1.05

According to the first specific example, the overall height or thickness of the antenna is very thin, but the dielectric constant of the dielectric substrate formed by layers L1 and L2 is greater than 2.

Radius R shown in FIG. 1B₁、R₂、R₃And R₄Respectively corresponding to the outer radius (R) of the annular dielectric layer₁) Outer radius of the annular patch (R)₂) Inner radius of the annular patch (R)₃) And the inner radius (R) of the dielectric layer₄). Radius R_iIs the distance between the central axis and the midpoint of the slot. Advantageously, said diameter (corresponding to twice the radius R)₂) Slightly larger than half the wavelength of the desired application.

With respect to achieving a similar design on a homogenous foam layer, the diameter size of the antenna may be reduced by about 30% and the thickness by about 60%. The main advantage of this first preferred embodiment is therefore that the resulting antenna is very thin in height, although somewhat less efficient than the subsequent solutions described hereinafter in relation to the second and third embodiments.

Fig. 2 is a cross-sectional view of a single antenna component according to a first variant of the second embodiment of the invention. Elements common to those of fig. 1A will not be described in detail.

The main difference between the aforementioned first embodiment and this second embodiment is the dielectric substrate placed between the annular patch radiating element 2 and the electrically conducting ground plane 4. In fact, in the second embodiment, the dielectric substrate is provided based on the sandwiched dielectric layers L21 and L22 composed of materials having different characteristics. The particular composition of the dielectric layers L21 and L22, with different dielectric constants and thicknesses, allows to synthesize the dielectric constant of the dielectric substrate between the annular patch 2 and the first ground plane 4, thus optimizing the dimensions of the antenna and its behaviour.

Previous studies have shown that the use of high dielectric constant substrates not only reduces the size of these antennas, but also affects the tilt of the cone beam. A disadvantage of this approach is that the use of a high dielectric constant substrate significantly reduces the antenna efficiency. Analysis of the radiation mechanism of the loop patch in the higher order modes shows that combining dielectric loss with poor combinations of the physical size of the antenna with free space wavelengths results in very inefficient antennas.

In the example shown, the media substrate is formed from a first layer of plastic L21 and a second layer of foam or air L22. The resulting dielectric constant of the dielectric substrate is then adjusted to a desired value. For example, it has been shown within the scope of the invention that the dielectric constant of the dielectric substrate is between 1 and 2 for a more efficient antenna. With a plastic layer having a dielectric constant greater than 2, and a foam layer having a dielectric constant close to 1, the dielectric constant of the dielectric substrate can be made between 1 and 2 by varying the height of the dielectric layers L21 and L22.

Fig. 5 is a top view of fig. 2, 3 and 4 showing the slot arrangement towards the annular patch radiating element. From this view it can be seen that the slot is not arranged exactly in the middle of the annular patch, but is moved to the inner circumference of the annular patch. Adjusting antenna matching by moving the slot along the loop patch. However, in order to optimize the reception of two circular polarizations, it is important that the two slots maintain an angle of 135 °.

Radius R₁And R₂Corresponding to the outer portions, respectively to the inner radius of the annular patch. Radius R_iCorresponding to the average radius of the groove about the central axis (D). Advantageously, the radius R₂Slightly greater than one quarter of the desired wavelength.

Fig. 3 is a cross-sectional view of a single antenna component according to a second variant of the second embodiment of the invention. As with fig. 2, only the new elements of this antenna assembly will be described in detail hereinafter.

The main difference with the antenna assembly shown in fig. 2 is also the placement of the first dielectric substrate between the annular patch radiating element 2 and the electrically conducting ground plane 4. In this second variation, the first dielectric substrate is comprised of three layers (L21-L23). Between the slots 7 (only one shown) etched in the ground plane 4 and the ring patch 2, a foam layer interlayer L22 is placed between two layers L21 and L23 of epoxy or plastic. In the example shown, the annular patch is etched directly on plastic layer L21, but the patch may also be etched on a very thin epoxy film.

As with fig. 2, a dielectric substrate (L21-L23) with a dielectric constant between 1 and 2 can increase antenna efficiency. Such a dielectric constant can be obtained by changing the heights of the dielectric layers L21, L22, and L23.

According to a preferred example of the second variant described above, an array of sizes of the different layers (L21-L23 and L3-L4) is given below. And also gives the dielectric constant (Dc), also called conductivity, of the layers.

Layer(s)	Material	Thickness (millimeter)	Dc
				21	Epoxy or plastic	0.8 to 5	4.4 or 2.3
22	Foam (or air)	From 0.5 to 5	1.05
				23	Epoxy or plastic	0.8 to 5	4.4 or 2.3
3	PTFE	0.5	3.0
				4	Foam (or air)	10	1.05

With a similar design implemented on a homogenous foam layer, the diameter size of the antenna can be reduced by about 20% and the thickness by about 45%. In particular, the multilayer dielectric substrate optimizes the size reduction of the annular patch for low elevation angles and allows a wider radiation beam than previously possible. The effective experimental value of the dielectric constant is between 1.7 and 1.9.

Fig. 4 is a cross-sectional view of a single antenna component according to a third variant of the second embodiment of the invention. This third variation is another variation of the first dielectric substrate placed between the annular patch radiating element 2 and the electrically conducting ground plane 4. In this third variant, in order to obtain a dielectric substrate with a dielectric constant that can be adjusted with the height of the different layers, and whose behaviour is more homogeneous, in particular with respect to the radiation pattern, said dielectric substrate is provided with five layers (L21-L25). In the example shown, the annular patch is etched directly on plastic layer L21.

Thus, between the slots 7 (only one shown) in the ground plane 4 and the ring patch 2, three plastic layers L21, L23 and L25 and two foam layers L22 and L24 are sandwiched. Each foam layer is embedded between two plastic layers. This combined dielectric substrate has been realized to further optimize the behavior of the antenna and to further reduce its size.

According to a preferred example of the second variant described above, an array of sizes of the different layers (L21-L25 and L3-L4) is given below. And also gives the dielectric constant (Dc), also called conductivity, of the layers.

Layer(s)	Material	Thickness (millimeter)	Dc
				21	Plastic material	1.8	2.3
22	Foam (or air)	1	1.05
				23	Plastic material	1.8	2.3
24	Foam (or air)	1	1.05
				25	Plastic material	0.8	2.3
3	PTFE	0.5	3
				4	Foam (or air)	5	1.05

With regard to the latter solution described with reference to fig. 3, the antenna is reduced in diameter by about 10% and in thickness by about 30%. In particular, the multilayer dielectric substrate further optimizes the size of the annular patch for low elevation angles and results in a wider radiation beam than previously. An effective experimental value for the dielectric constant is about 1.9.

Fig. 6 is a cross-sectional view of a single antenna assembly according to a third embodiment of the present invention. In this third embodiment, the main difference from the two first embodiments is the feeding means, which is electromagnetically coupled to the ring patch, instead of being coupled through a slot.

Away from the top of the antenna component 1, we find downwards a ring patch radiating element 2, which is etched on a thin epoxy film (not shown, corresponding to L1 in the first embodiment) or directly on a plastic layer L21 of the first dielectric substrate. The first dielectric substrate includes at least two layers (L21-L23). In the example shown, the dielectric substrate is formed by a sandwich of one epoxy or epoxy and foam layer L22 placed between two plastic layers L21 and L23. Below the first dielectric substrate we find a second dielectric substrate L3, advantageously formed of a layer of PTFE. The PTFE layer is metallized on both surfaces 4 and 5 and will be used for etching on the underlying microstrip circuit (feed line, connector, active element, etc.). At the top, the metallization forms a first electrical ground 4 in which at least one, preferably two small circles 10 (not shown) are etched to allow vertical metal pins 11 to pass through. Another feed line 12 is etched in the intermediate epoxy layer L22 of the first dielectric substrate. The vertical metal pins 11 are connected between the feed lines 6 at the metallized bottom of the PTFE layer L3 and the feed lines 12 embedded in the first dielectric substrate. Thus, the signal is electromagnetically coupled (non-electrically contacted) between the upper feed line 12 and the annular patch radiating element 2.

Finally, under the bottom metallization 5, a foam or air layer L4 is provided, together with a second conductive ground plane 8, as a back shield. The thickness and diameter of this foam layer L4 can be reduced and thus the overall size of the antenna can be reduced. The efficiency of the antenna will be slightly reduced due to the reduced size, but this loss can be partly compensated for due to the slightly higher efficiency of the electromagnetic coupling feed than the slot coupling feed. The posts here are much shorter than the metal feed posts used in the prior art document US 2003/0210193 and do not affect the radiation pattern of the antenna.

According to a preferred example of the above third embodiment, an array of sizes of the different layers (L1, L21-L23, and L3-L4) is given below. And also the dielectric constant (Dc), also called conductivity, of the different layers.

Layer(s)	Material	Thickness (millimeter)	Dc
				L1	Epoxy (optional layer)	0.5	4.4
L21	Plastics only or plastics + epoxy	0.8 to 5	2.3
				L22	Epoxy + foam or epoxy only	0.1 to 2-3	4.4
L23	Plastic material	0.8 to 5	2.3
				3	PTFE	0.5	3
4	Foam (or air)	1 to 5	1.05

Note that the electromagnetic coupling is less affected by the support of the antenna (e.g., the roof of a vehicle) than the slot coupling, and therefore, the height of layer L4 can be further reduced.

Fig. 7 is a partial top view of a first multi-system antenna component 21 according to any one of the previous embodiments of the invention. In this multi-system antenna, antennas are provided for at least two and preferably more than two applications. A very interesting feature is the overall size of such a multi-system antenna, which is about the same size as the single-application antenna structure described hereinbefore. It is therefore well suited to mobile communication systems which always require more functionality and less space to implement.

In the example shown, the multi-system comprises a first antenna structure comprising a ring-shaped patch radiating element 22 slot-coupled or electromagnetically coupled (solution not shown in fig. 7) to a feed line 26 via a slot 27. When used in the second order resonance mode, the first antenna structure has a cone shaped radiation pattern that is very useful and effective for low elevation mobile satellite applications. It is known that the use of two slots 7 angularly displaced at an angle of 135 ° ensures very efficient reception of right-hand and left-hand circular polarizations used by mobile satellite applications like WorldSpace.

In addition to this first antenna structure, the multi-system antenna assembly 21 further comprises at least one second antenna structure for receiving signals from another application or, ultimately, from a transponder of a first desired application.

For example, the second antenna structure comprises a disc-shaped patch radiating element 33, which is placed concentrically, for example, within the inner radius of the annular patch, and is preferably coplanar with the annular patch 22 in a plane perpendicular to the central axis (D), and which is advantageously designed on the same substrate structure as the annular patch. This circular patch radiating element 33 resonates in the fundamental mode.

While both metallized surfaces of the PTFE layer are etched to obtain in particular the microstrip circuit 34 of the first antenna (as described earlier), a second antenna microstrip circuit 35 is etched on the bottom metallization of the PTFE layer and an opening, e.g. a slot 36, is etched on the upper metallization facing the disc-shaped patch radiating element 33. Thus, the circular patch radiating element 33 is also fed through slots 36, 37 in the ground plane and is dual circularly polarized to operate with Right Hand Circular Polarization (RHCP) used by navigation systems such as the Global Positioning System (GPS) and the future galileo system, and Left Hand Circular Polarization (LHCP) used by two-way mobile communications systems such as THURAYA.

Fig. 8 is a cross-sectional view of a second multi-system antenna component according to the first embodiment of the invention. In this second multi-system antenna assembly 41, at least one further antenna is further provided in addition to the first antenna patch radiating element 42 already described with reference to fig. 1A and 1B. A micro GPS antenna 44 may be integrated in the void space 43 within the first annular dielectric substrate 45. Advantageously, a third antenna, such as a radio FM antenna 46, may be rolled around the antenna assembly 41. The advantage of this solution is that the GPS and FM antennas are available at a very low price and can be easily mounted on the microstrip patch antenna described according to the first embodiment.

Fig. 9A-9B show two possible shapes of the antenna component according to the first embodiment and the first dielectric substrate of the first multi-system antenna component. We find a dielectric layer L2 placed between the annular patch radiating element 2 and the electrically conducting ground plane 4, wherein the opening is not shown.

In fig. 9A, the dielectric layer L2 is generally seen to be cylindrical, at the periphery of which at least one annular recess is arranged.

In fig. 9B, the dielectric layer L2 is a truncated cone shape, the large base is provided on the side of the annular patch 2, and the small base is provided on the side of the ground plane 4.

Both solutions allow to adjust the dielectric constant of the dielectric layer provided between the annular patch and the ground plane.

Fig. 10A-10C show different possible shapes of the slot. In order to obtain an optimized slot coupling between the feed line and the annular patch, it is important that the entire surface covered by the slot is facing the annular patch completely.

However, since an elongated slot is required to couple energy from the microstrip to the patch radiating element, the size required for a standard rectangular slot is too large relative to the width of the annular patch and, therefore, the degree of coupling between the excitation ports will increase, thereby degrading the quality of the circular polarization. Therefore, to avoid this problem, some special slots with folding arms have been designed. Each slot is folded until it completely faces the annular patch radiating element.

To this end, fig. 10A shows a first example of a groove having an inverted H-shape. Fig. 10B shows a second example of the C-shaped groove. Fig. 10C shows a third example of a slot having a mirror T-shape.

As a final consideration, it is noted that for the same resonance mode, a circular patch allows a smaller antenna to be designed than a circular patch. In fact, in a loop antenna of a higher order mode, the field density of the central portion of the patch is low. For this reason, this portion of the antenna can be cut out to obtain a loop shape without affecting the performance of the antenna; the cut-out portions are then used for other applications. On the other hand, the electrical length of the antenna can be increased, thereby lowering the resonant frequency of the antenna.

Finally, it is to be understood that the above-described embodiments are illustrative of the many possible specific embodiments, which are indicative of the principles of the invention. In view of these teachings, it will be readily appreciated by those skilled in the art that various modifications may be made to the disclosed embodiments without departing from the spirit or scope of the invention.

Claims (21)

1. A microstrip patch antenna (1) for mobile satellite communications, comprising:

a first electrically conducting ground plane (4) having two slots (7),

at least one annular patch radiating element (2) having a central axis (D),

at least one first dielectric layer (L2; L21-L22; L21-L23; L21-L25), which is located between said first electrically conducting ground plane and said patch radiating element,

two feed lines (6) slot-coupled to the patch radiating element for supplying signal energy to or receiving energy from the patch radiating element in a non-contact manner through the slots, and

a second dielectric layer (L3) between the feed line and the first electrically conductive ground plane, wherein the antenna further comprises:

a second ground plane (8) and a third dielectric layer (L4) between the second ground plane and the feed line, and wherein,

the two slots (7) are placed along the annular patch and are angled with respect to the central axis so as to receive left-hand and right-hand circularly polarized signals.

2. The microstrip patch antenna according to claim 1, wherein said at least one first dielectric layer (L2; L21-L22; L21-L23; L21-L25) is located between said slot and said patch radiating element.

3. The microstrip patch antenna according to claim 1, wherein said slot is 135 ° with respect to said central axis (D).

4. The microstrip patch antenna according to any one of claims 1 to 3, wherein each of said slots is folded until fully facing said annular patch radiating element, said slot being C-shaped or mirror T-shaped.

5. The microstrip patch antenna according to claim 1, wherein said antenna is cylindrical and wherein the outer radius (R) of said patch radiating element₂) Greater than one quarter of the desired wavelength.

6. The microstrip patch antenna according to claim 1, wherein said first dielectric layer has a circular geometric cross-section defining an inner void region (3).

7. The microstrip patch antenna according to claim 1, wherein said at least one first dielectric layer is comprised of at least one plastic layer and said second dielectric layer is comprised of polytetrafluoroethylene.

8. The microstrip patch antenna according to claim 1, wherein a thin epoxy layer (L1) is placed between said first dielectric layer and said patch radiating element.

9. The microstrip patch antenna according to claim 1, wherein said first dielectric layer is frusto-conical having a small base and a large base, said large base being disposed on said patch radiating element side and said small base being disposed on said first electrically conducting ground plane side.

10. The microstrip patch antenna according to claim 1, wherein said first dielectric layer is cylindrical with at least one annular recess disposed at the periphery of the cylinder.

11. The microstrip patch antenna according to claim 1, wherein at least two dielectric layers (L21-L22; L21-L23; L21-L25) are placed between said first electrically conducting ground plane and said patch radiating element, comprising at least one plastic layer (L21) and one foam layer (L22), and wherein the equivalent dielectric constant of said at least two dielectric layers is strictly greater than 1 and strictly less than 2.

12. The microstrip patch antenna according to claim 11, wherein said dielectric constant is between 1.7 and 1.9.

13. The microstrip patch antenna according to claim 11, wherein said at least two dielectric layers are three dielectric layers, comprising two plastic layers (L21, L23) and one foam layer (L22) interposed between said plastic layers.

14. The microstrip patch antenna according to claim 11, wherein said at least two dielectric layers are five dielectric layers (L21-L25).

15. The microstrip patch antenna according to claim 1, further comprising two additional slots, symmetrically arranged with respect to said central axis (D).

16. A multi-system antenna (21) for mobile communications, comprising:

a first electrically conducting ground plane having at least a first slot (27) and at least a second slot (36, 37),

an annular patch radiating element (22) and a circular patch radiating element (33) concentrically arranged with and coplanar with said annular patch radiating element having a central axis (D),

at least one first dielectric layer disposed between said first electrically conductive ground plane and said annular and circular patch radiating elements,

at least first and at least second feed lines (26, 38) slot-coupled to the patch radiating element for providing signal energy to or receiving signal energy from the annular and circular patch radiating elements in a non-contact manner through the at least first and at least second slots, respectively,

a second dielectric layer disposed between the at least first and at least second feed lines and the first electrically conducting ground plane, and wherein,

the at least a first slot (27) is positioned along the annular patch and is angled with respect to the central axis to receive right and left hand circularly polarized signals of a first application with the annular patch radiating element.

17. The multi-system antenna according to claim 16, wherein said at least one first dielectric layer is placed between said at least first and second slots and said annular and circular patch radiating elements.

18. The multi-system antenna according to claim 16, further comprising: a second ground plane and a third dielectric layer between the second ground plane and the feed line.

19. The multi-system antenna according to claim 16 or 18, wherein two of said first electrically conducting ground planes have two second slots (36, 37) and said two second slots (36, 37) are angled with respect to said central axis so as to obtain a second applied left-hand circular polarization and a third applied right-hand circular polarization signal.

20. A multi-system antenna comprising the microstrip patch antenna according to claim 6, wherein it further comprises another antenna placed in said inner void region of said microstrip patch antenna.

21. The multi-system antenna according to claim 20, further comprising a third antenna formed by an elastic substrate wrapped around said microstrip patch antenna.